1. Field of the Invention
The present invention relates to a sheet guide and an image recording apparatus. For instance, at the time of transporting a sheet such as a recording paper, there is a structure of a sheet guide which positions the sheet in a direction intersecting a transporting direction. Such sheet guide is typically used in an automatic document feeder installed in an image recording apparatus, and other document trays and a paper feeding tray which supports the recording paper.
2. Description of the Related Art
An image recording apparatus such as a copy machine and a printer includes a tray on which a plurality of sheets (basically, documents and recording papers) is piled up. Sheets placed on the tray, upon being separated one-by-one, are dispatched in a predetermined direction of transporting, and an image processing such as an image reading and an image recording is carried thereon. For a favorable image processing to be carried out, a sheet is to be prevented from being passed obliquely when transported. For this, the tray has hitherto been provided with a sheet guide.
The sheet guide includes a guide which guides the sheet along the transporting direction. The guide has a pair of guide surfaces along the transporting direction, and the sheet is positioned along the guide surfaces. There are two types of methods (modes) for positioning the sheet. These two methods are so-called side-register type and a center-register type. In the side-register type, one of the guide surfaces is fixed, and one side of the sheet makes a contact with the fixed guide surface. In a state of one side of the sheet making a contact with one guide surface, the other guide surface comes closer or moves away from the fixed guide surface, and makes a contact with the other side of the sheet. Accordingly, the sheet is positioned with the fixed guide surface as a base (reference position). Moreover, in the center-register type, guide surfaces in pair come closer or move away mutually, and the two guide surfaces make a contact with the two sides of the sheet. Accordingly, the two sides of the sheet are sandwiched between the two guide surfaces, and the sheet is positioned with a center of the two guide surfaces as a base. A conventional mechanism for bringing closer or moving away a pair of side guides is a rack and pinion mechanism.
In both the types, since a prompt positioning of a sheet is realized, it is sought that the guide surfaces in pair come closer or move away easily according to the sheet which is to be transported. On the other hand, for a favorable image processing to be carried out on the plurality of sheets, the movement of the guide surfaces has to be regulated during continuous transporting of the sheets. Particularly, in the center-register type provided with the rack and pinion mechanism, since the guide surfaces in pair are susceptible to come closer and move away relatively, regulation of the movement of the guide surfaces has been sought strongly. Therefore, in the sheet guide which has hitherto been used, a sliding washer has been provided to a pinion. Accordingly, a sliding resisting power (sliding resistance) is generated (developed) when the pinion rotates, and the guide surfaces in pair have been regulated to move easily.